<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* .box{
           width: 200px;
           height: 200px;
           background-color: pink;
           clip-path: polygon(0 0,200px 0,0 200px);
        } */
      /* .box{
        width: 50px;
        height: 0px;
        
        /* border: 50px solid #000; */
        /* border-top: 50px solid #000;
        border-top-color: transparent;
        border-right-color: transparent;
        border-bottom-color: transparent;

      } */ 

      .box{
        width: 100px;
        height: 100px;
        background-color: #df3c3c;
        border-radius: 50%;
        clip-path: polygon(0 0, 100px 0, 50px 50px);
      }
    </style>
</head>
<body>
    <div class="box">

    </div>
    
</body>
</html>